Disclosed herein is an apparatus and method that operates a flattener in an ink-based printing apparatus.
Solid inks and ultraviolet gel inks can be jetted directly onto cut sheet media in printing devices using ink jet direct marking technology. In such a process, after ink has been deposited on a media sheet, it is expected that the ink must be thermally leveled by a leveler and then spread to a final dot size in a flattener device, such as in spreader nip. The spreader nip includes a heated spreader roll which contacts the ink and a backing pressure roll that supplies the necessary 1.0-1.5 Kpsi nip pressure. In order to prevent ink on the media sheets from offsetting to the spreader roll, the spreader roll has a silicone oil film maintained on its surface.
This oil film will transfer from the spreader roll surface to the pressure roll surface when there is no sheet in the nip, such as is the case during an inter-copy gap between sheets. Oil from the pressure roll surface is transferred to the backside of the next media sheet it enters the spreader nip. This means that when an image is spread on a first side of a media sheet when it passes through the spreader nip, the second side becomes contaminated with oil.
This causes an undesirable result for duplex operation where images are printed on both sides of a media sheet. The problem is that oil contamination of the second side of a media sheet leads to loss of ink adhesion to the second side. One possible solution is to cam a flattener nip, such as the spreader nip or a transfix nip, open and closed between each sheet during duplex jobs so that oil is not allowed to transfer from the spreader roll to the pressure roll during inter-copy gaps. Unfortunately, that solution results in a loss of duplex productivity. This becomes impractical when such camming is used in printing devices that require higher productivity, such as beyond 150 ppm.
Thus, there is a need for a method and apparatus that operates a flattener in an ink-based printing apparatus.